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This invention relates to semiconductor devices and methods of manufacturing semiconductor devices, and more particularly, to semiconductor devices and methods of manufacture utilizing charge depletion regions to enhance Schottky diode behavior.
Schottky semiconductor devices traditionally include an N+ low resistivity substrate, an Nxe2x88x92 high resistivity epitaxial layer adjacent to the N+ substrate, and a barrier metal adjacent to the Nxe2x88x92 layer, wherein a Schottky barrier or Schottky junction is formed between the Nxe2x88x92 layer and the barrier metal. Schottky diodes also typically include a guard ring adjacent to the perimeter of the barrier metal and located in the Nxe2x88x92 layer. Traditional Schottky semiconductor devices experience a desirable low forward voltage drop and an undesirable high reverse leakage current. In other words, the voltage drop across the Schottky diode during the current transmission period of the diode""s operation is desirably low, but, during the time when the diode is not expected to conduct current, the Schottky diode can experience a conduction of current. The nature of a standard Schottky barrier device is such that when the Schottky barrier height between the Nxe2x88x92 layer and the barrier metal is large, the reverse current is small. Conversely, when the Schottky barrier height is small, the reverse leakage current is large. Normal current flow is in the direction of the anode to the cathode, in other words, from the barrier metal to the semiconductor. This current flow is primarily from electrons flowing from the semiconductor into the metal. Also, in regards to a traditional Schottky device, with increased temperature, leakage current increases exponentially. Thus, temperature operating ranges are restricted to strictly defined temperature ranges.
PN diodes, which include an N layer adjacent to a P layer, have the following benefits and disadvantages. In a forward current flow, from the P layer to the N layer, current flows through the PN diode after a minimum voltage is reached. This voltage can be, for example, 0.7  volts. The voltage drop will continue to increase as the forward current increases. Traditional PN semiconductor devices experience this high forward voltage drop and a lower reverse leakage current. In other words, the voltage drop across the PN diode during the current transmission period of the diode""s operation is undesirably high, but, during the time when the diode is not expected to conduct current, the PN diode experiences a very low conduction of current compared to a Schottky device. In a reverse current flow, the PN diode appears as a high resistance to the flow and, thus, only a small amount of reverse current flows through the diode. Also, the maximum operating temperature rating is usually higher for a PN diode than for a Schottky diode. Thus, each type of device has characteristics that make it preferable for different applications.
To remedy large reverse leakage current in semiconductor devices, designers produced a hybrid of PN devices and Schottky devices. These hybrids consist of devices with areas of P+ material adjoining barrier metal. By this addition of P+ material in contact with the barrier metal of a Schottky device, designers have experienced some benefits by seeing a reduction in the reverse leakage current, but have also sacrificed desirable characteristics by significantly consuming the Schottky barrier area by P+ doped regions, thus not creating an ideal tradeoff between a desired low forward voltage drop and a desired low reverse leakage current.
There is, therefore, provided in the practice of the invention a novel semiconductor device, which provides for an improved low forward voltage drop and a low reverse leakage current. The semiconductor device broadly includes a first layer of semiconductor material of a first conductivity type. A region of semiconductor material of a region conductivity type is positioned such that the first layer of semiconductor material surrounds the region. A second layer of semiconductor material of a second conductivity type is adjacent to, contiguous with, the first layer.
In a preferred embodiment, the region conductivity type is P type and the first and the second conductivity types are N type. Preferably, a conductor is in contact with the second side of the second layer of semiconductor material and a barrier metal is adjacent to the second side of the first layer of semiconductor material.
It is further contemplated in the practice of a preferred embodiment of the invention that the Schottky barrier area be relatively free from semiconductor material of P type, with the exception in an embodiment that a guard ring area can be in contact with the P type material of the region of semiconductor material.
An object of the present invention is to provide an improved Schottky device without diminishing the area of the Schottky barrier and retaining the benefits of a PN diode. The present invention has an improved high temperature performance with a low reverse leakage current and a low forward voltage drop.